The present invention relates to an open circuit hydraulic system and, more specifically, a flow sharing priority circuit for an open circuit hydraulic system.
Open circuit hydraulic systems are commonly used to drive a plurality of subsystems attached thereto. For example, an open circuit hydraulic system provided on heavy machinery may be used to drive the steering system, the fan motor, and a plurality of other components of the heavy machinery.
Open circuit hydraulic systems typically use priority valves to ensure that certain subsystems receive adequate hydraulic flow from the open circuit hydraulic pump. For instance, in an open circuit hydraulic system driving a critical system, such as a steering system, and a plurality of non-critical auxiliary systems, a priority valve may be used to ensure that the flow requirements of the critical system are satisfied before supplying hydraulic flow to the auxiliary systems. As such, priority valves ensure that the auxiliary systems do not starve off hydraulic flow from a critical system should the open circuit pump not be able to meet all of the demands of the system.
One disadvantage of conventional priority valves is that they tend to experience some undesired shift with changes in flow between the priority and auxiliary systems. Typical priority valve designs comprise a single spool or valve actuating element. It is inherent in this design that the valve spool will tend to shift when excess flow is provided from the priority system to the auxiliary system, resulting in undesired changes in the pressure and flow to the priority system. For instance, in an open circuit system driving a priority steering system and an auxiliary fan motor, a user will notice a small undesired jerk in the machine's steering wheel as the fan motor turns on or off.
It is therefore a principal object of this invention to provide a priority valve that prevents undesired changes in the pressure and flow of the priority system upon activation or deactivation of the auxiliary system.
A further object of this invention is to provide a flow sharing priority circuit that utilizes two independent priority valves.
These and other objects will be apparent to those skilled in the art.